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- Bitzén, Ulrika, et al.
(författare)
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Dynamic elastic pressure-volume loops in healthy pigs recorded with inspiratory and expiratory sinusoidal flow modulationRelationship to static pressure-volume loops.
- 2004
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Ingår i: Intensive Care Medicine. - : Springer Science and Business Media LLC. - 0342-4642 .- 1432-1238. ; 30:3, s. 481-488
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The objective was to analyse relationships between inspiratory and expiratory static and dynamic elastic pressure-volume (P-el/V) curves in healthy pigs. Design: The modulated low flow method was developed to allow studies also of the expiratory P-el/V curves. Static P-el/V (P-el,P-st/V) and dynamic P-el/V (P-el,P-dyn/V) loops were studied in healthy pigs. Setting: Animal research laboratory in a university hospital. Material: Ten healthy anaesthetised and paralysed pigs. Interventions and measurements: A computer controlled a Servo Ventilator 900C with respect to respiratory rate, inspiratory flow and expiratory pressure to achieve a sinusoidal modulation of inspiration and expiration for determination of P-el,P-dyn/V loops from zero end-expiratory pressure (ZEEP) and from a positive end-expiratory pressure (PEEP) of 6 cmH(2)O to 20, 35 and 50 cmH(2)O. The same system was used for studies of P-el,P-st/V loops with the flow-interruption method from ZEEP and PEEP to 35 cmH(2)O. Recordings were analysed with an iterative technique. Results: The feasibility of automated determination of P-el,P-dyn/V loops was demonstrated. Differences between P-el,P-dyn/V and P-el,P-st/V loops were explained by viscoelastic behaviour. P-el,P-st/V loops recorded from PEEP to 35 cmH(2)O showed no significant hysteresis, indicating a non-significant surface tension hysteresis. P-el,P-dyn/V loops from PEEP and both P-el,P-st/V and P-el,P-dyn/V loops from ZEEP to 35 cmH(2)O showed hysteresis. This indicates that lung collapse/re-expansion caused P-el/V loop hysteresis which, in P-el,P-dyn/V loops, was augmented by viscoelastic behaviour. Conclusions: Viscoelasticity influences P-el,P-dyn/V curves. Hysteresis caused by surface tension merits re-evaluation. Lung collapse and re-expansion may be indicated by hysteresis of P-el/V loops.
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| 5. |
- Aleksandrov, D., et al.
(författare)
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Halo excitations in fragmentation of He-6 at 240 MeV/u on carbon and lead targets
- 2000
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Ingår i: Nuclear Physics A. - 0375-9474. ; 669:1-2, s. 51-64
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Tidskriftsartikel (refereegranskat)abstract
- Dissociation of a 240 MeV/u beam of He-6, incident on carbon and lead targets, has been studied in kinematically complete experiments to investigate low-lying excitation modes in the halo nucleus He-6. It is shown that alignment effects characterize the inelastic scattering and allow an unambiguous assignment of the spin of a narrow resonance observed in the excitation energy spectrum. The differential cross sections for the He-6 inelastic scattering on carbon and lead targets were deduced from the measured moments of the two neutrons and the a-particle. An analysis of these distributions shows that quadrupole and, possibly, monopole excitations characterize the hadronic interaction, while the dipole mode is dominating in Coulomb dissociation. Neither theoretically predicted new resonance states in He-6 nor nuclear excitation of a dipole mode were found. Direct evidence has been obtained for strong suppression of Coulornb post-acceleration in direct Coulomb breakup in a lead target.
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| 7. |
- Almquist, H, et al.
(författare)
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Performance of simultaneous emission-transmission systems for attenuation-corrected SPEct: a method for validation applied to two camera systems
- 2001
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Ingår i: Nuclear Medicine Communications. - 1473-5628. ; 22:7, s. 759-766
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Tidskriftsartikel (refereegranskat)abstract
- Several commercially available systems for attenuation correction in single photon emission computed tomography (SPECT) based on a transmission scan have been introduced that vary in performance. A test procedure for attenuation correction in SPECT is described and applied to two principally different gamma camera systems (the Siemens Multispect 3 triple-headed system [3HS] and the ADAC Genesys Vertex double-headed system [2HS]). The test procedure was based on geometrically well-defined phantoms. A torso phantom was used to illustrate the attenuation correction methods. The test procedure can be used without detailed knowledge of or access to the algorithms used for attenuation correction. The influence on the transmission measurement of radioactivity in a phantom was higher for the 2HS than for the 3HS. The 3HS produced satisfactory attenuation maps and corrected emission count rates to a constant value independent of phantom density and size. With the 2HS, there was a progressive decrease in the correction of emission count rates with increasing phantom density, and about 30% lower corrected count rates in the large compared with the small phantom. A decrease in measured attenuation coefficients in the vicinity of an emission source was demonstrated in large but not small phantoms. A likely explanation is erroneous correction of downscatter into the transmission energy window. This study demonstrates the need for independent evaluation of systems for attenuation correction in SPECT.
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| 8. |
- Axelsson, L., et al.
(författare)
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Deriving the angular variation of p(parallel to)-distributions for halo neutrons with robust statistics
- 2001
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Ingår i: Nuclear Physics A. - 0375-9474. ; 679:3-4, s. 215-230
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Tidskriftsartikel (refereegranskat)abstract
- The longitudinal neutron momentum distribution from core breakup of Li-11 and Be-11 have been measured at 29.9 MeV/u and 38.5 MeV/u, respectively. Separate measurements on Li-9 and Be-10 allowed extraction of the halo neutron distribution. The shapes of the distributions are analyzed using robust and descriptive statistics, For both isotopes the shape is changing with angle. (C) 2001 Elsevier Science B.V. All rights reserved.
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